Check to see if the hot solenoid is getting power when it should be. I'm assuming there is water coming to the solenoid valve.
FIRST WE TURN OFF THE POWER...........
If your reverse the "live" wires [most-likely NOT white, green or yellow] to the hot and cold solenoids, does the hot water now flow?
(....just a reminder....... it should, in this temporary state, flow when "COLD" is selected, natch.)
If hot still does not flow, but the cold does flow (when hot is selected) while the wires are still reversed, you may have a bad "neutral".
Now reverse 'em back!